Implementation of OGC Web Coverage Service Using HDF5/HDF-EOS5 as the Base File Format

Page 1 CSISS LCenter for Spatial Information Science

and Systems11/08/2007

Implementation of OGC Web Coverage Service Using HDF5/HDF-EOS5 as the Base

File Format

Peichuan Li, Ph.D.

Liping Di, Ph.D.

Genong (Eugene) Yu, Ph.D.

Center for Spatial Information Science and Systems (CSISS)

George Mason University

6301 Ivy Ln, Suite #620

Greenbelt, MD 20770

Emails:(pli4,ldi,gyu)@gmu.edu

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Contents

• Introduction• Methodology • Samples of system implementation • Discussion and Conclusion

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Introduction

1. Activities & Purpose

– The requirement for the ongoing Sensor Web project conducted at CSISS ;

– Research its possibility for WCS to serve new kinds of base data that it is different from what we have previously done;

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Introduction (Cont.)

2. Objectives – Final Goal:

• To implement a Web Coverage Service (WCS) for describing and delivering multidimensional geospatial coverage data in HDF-EOS 5/HDF-5 format. The services followed OGC WCS Specification 1.1.0. [1]

• The Web Coverage Service (WCS) implemented provides the Transaction operation.[2] The transaction provides the flexibility of re-serving derived results in standard geospatial services.

– Phrases:• Phrase 1:

– Focus on Aura/HIRDSL L2(hdfeos5) base data;– Implement general operations of WCS. i.e. getCoverage,

getCapabilites, DescribeCoverage…;– Provide he5 Swath and netCDF responding to client’s request;

• Phrase 2:– Add Transaction operation;– Provide Aura / plain hdf5 base data support;

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3. About Aura HIRDLS data [3]

– HIRDLS is an infrared limb-scanning radiometer designed to sound the upper troposphere, stratosphere, and mesosphere to determine temperature;

– HIRDLS measures the concentrations of O3, H2O, CH4, N2O, NO2, HNO3, N2O5, CFC11, CFC12, ClONO2, and aerosols;

– Locations of polar stratospheric clouds and cloud tops. – The goals were to provide sounding observations with

horizontal and vertical resolution superior to that previously obtained;

– To observe the lower stratosphere with improved sensitivity and accuracy; and to improve the understanding of atmospheric processes through data analysis, diagnostics, and use of two- and three-dimensional models.

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• About AutoChem [4]

– AutoChem is a NASA release software that constitutes an automatic computer code generator and a documenter for chemically reactive systems written by David Lary between 1993 and the present. It was designed primarily for modeling atmospheric chemistry, and in particular, for chemical data assimilation .

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Methodology

1. Architecture

Web user

AutoChem System

Other App. System

WCS_TServer

Aura/HIRDLSData Files

Web Protocol Web Protocol

WCS Comm. Interface

WCS_T Interface

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Methodology

– The Component diagram

WCS2HIRDLS

WCS_Parser

CoverageSet

CGI

DataDrivers

*

* * *

* *

**

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Methodology (cont.)

– Sequence diagram

cgi:CGI wcs:WCS2HIRDLS coverage:HIRDLS_Coverage swath:DataDriver DataField:HE5Swath geoFields:HE5Swath

getCoverage(string requestedmessage)

runParser()

parser:WCSParser

getEnviromentVar()

CGIenvVar

requestedMessages

getCoverage() inquireDriver

swathDriver

createDataField()

createGeoField()

extractData()

inquireLocation

geolocation

dataBuffer

ouputSwath()

writeDataField()

writegeoField()

outputFile

getCoverageRespond

XMLRespond

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Methodology (cont.)

2. The difficulties to be solvedA. Representing, defining and restoring of the Line string

coverage [5]

• The definition of OGC Coverage:

– GIS coverages (including the special case of Earth images) are two- (and sometimes higher-) dimensional metaphors for phenomena found on or near a portion of the Earth’s surface.

– A coverage is a special case of (or a subtype of) feature.

– A feature with geometry has one or more properties taking values that are OpenGIS geometries (as defined in Topic 1, and in the Implementation Specifications.)

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Methodology (cont.)

• The coverage we used from HE5/HIRDLS is different from what we met previously. Geolocation information is based on line string geometry, in contrast to image and grid coverage. The geolocation and other location information were mapped by “Time” information indirectly.

(Source comes from [6])

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Methodology (cont.)

– Define an abstract data model (ADM) to present coverage with line string geometry in memory, mapping He5/HIRDLS Swath data to ADM, in addition to manipulate and process coverage on ADM.

– Dataset in ADM is a one/two (not more than two) dimension array. One of the dimensions is nTime dimension associated with Time and then mapped to Longitude/Latitude indirectly;

– One coverage is identified by its name ID and correspond to one Swath data field in HIRDLS data file.

e.g. HIRDLS2_v2.02.07-c3_2007d053.he5:SWATH:HIRDLS:O3

File Name Data TypeSwath nameData Field name

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B. Sub-setting operation for this particular kind of coverage

– Domain sub-setting:• We use Time sequence parameter to process Domain

sub-setting requested from user. The Domain sub-setting by geographic Bounding Box will be implemented in future. The extent of nTime is about 24h one day that are restricted by HIRDLS data. Time granule is one second (the time frame and representation followed Aura/HIRDLS data production specification).

Methodology (cont.)

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Methodology (cont.)

– Range sub-setting:• Range sub-setting extracts data on non-nTime

dimensions that are defined in ADM of coverage. It will depend on available number of dimensions and range of its value.

• The parameter that client requested for range sub-setting is defined by WCS 1.1.0 spec.

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Methodology (cont.)

– Output format:• For the reason of special coverage to be defined, the

restore file format for outputting coverage adopts he5/Swath and NetCDF format. Another reason to adopt the he5/Swath is due to the specific requirement of AutoChem application.

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Methodology (cont.)

C. Strategy of system design and development1. Based-on object-oriented design and programming

2. WCS_T request messages follow OGC WCS_T 1.1.0 Specification.

3. Wrap he5 c interface into c++ implementation class

4. Platform of development, testing and running;

1. eclipse

2. Linux

5. Utilize open source software and tools

1. expat and scew libraries for XML parser

2. Hdf5 1.6.6, hdf-eos 5.1.10, netCDF 3.6.2 c/c++ lib

3. Other required c/c++ lib and tools

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Samples of system implementation

• Current constraints of services routines: – Base data must be Aura/HIRDLS.– Domain sub-setting only supports Temporal

Period request.– Output format only supports he5 and netCDF.– For the sake of research, services routines only

complete GetCoverage operation up to now.

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Samples of system implementation (Cont.)

• Samples for “Get Method”:– Sample 1: with Domain and Range sub-setting

http://data.laits.gmu.edu:8080/cgi-bin/he5Swath?SERVICE=WCS&VERSION=1.1.0&REQUEST=GetCoverage&IDENTIFIER=HIRDLS2_v2.02.07-c3_2007d053.he5:SWATH:HIRDLS:O3&TimeSequence=446257000.0000/446300000.0000&FORMAT=image/hdfeos5&RangeSubset=O3:NONE[Pressure[348.070,316.228,261.016]]

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– Sample 2: with Range sub-setting and without Domain sub setting

http://data.laits.gmu.edu:8080/cgi-bin/he5Swath?SERVICE=WCS&VERSION=1.1.0&REQUEST=GetCoverage&IDENTIFIER=HIRDLS2_v2.02.07-c3_2007d053.he5:SWATH:HIRDLS:O3&FORMAT=image/hdfeos5&RangeSubset=O3:NONE[Pressure[348.070,316.228,261.016]]

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– sample 3: with Domain sub-setting and without Range sub-setting

http://data.laits.gmu.edu:8080/cgi-bin/he5Swath?SERVICE=WCS&VERSION=1.1.0&REQUEST=GetCoverage&IDENTIFIER=HIRDLS2_v2.02.07-c3_2007d053.he5:SWATH:HIRDLS:O3&TimeSequence=446257000.0000/446300000.0000&FORMAT=image/hdfeos5

– sample 4: without Domain and Range sub-setting

http://data.laits.gmu.edu:8080/cgi-bin/he5Swath?SERVICE=WCS&VERSION=1.1.0&REQUEST=GetCoverage&IDENTIFIER=HIRDLS2_v2.02.07-c3_2007d053.he5:SWATH:HIRDLS:O3&FORMAT=image/hdfeos5

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• Post Method:– WCS XML Request Message

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Samples of system implementation (Cont.) - request

<?xml version="1.0" encoding="UTF-8"?><GetCoverage xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://www.opengis.net/wcs/1.1 http://www.opengis.net/gml" xmlns="http://www.opengis.net/wcs/1.1" xmlns:ows="http://www.opengis.net/ows" xmlns:owcs="http://www.opengis.net/wcs/1.1/ows" xmlns:gml="http://www.opengis.net/gml" service="WCS" version="1.1.0"><owcs:Identifier>HIRDLS2_v2.02.07-c3_2007d053.he5:SWATH:HIRDLS:O3</owcs:Identifier><DomainSubset>

<wcs:TemporalSubset><wcs:TimePeriod>

<wcs:BeginPosition>446257000.0000</wcs:BeginPosition><wcs:EndPosition>446300000.0000</wcs:EndPosition>

</wcs:TimePeriod></wcs:TemporalSubset>

</DomainSubset><RangeSubset>

<FieldSubset><owcs:Identifier>O3</owcs:Identifier><InterpolationType>None</InterpolationType><AxisSubset>

<Identifier>Pressure</Identifier><Key>348.07000000</Key><Key>316.22800000</Key><Key>261.01600000</Key>

</AxisSubset></FieldSubset>

</RangeSubset><Output format="image/hdfeos5"></Output>

</GetCoverage>

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Samples of system implementation (Cont.) - response

• WCS XML Respond

<?xml version="1.0" encoding="UTF-8"?> <wcs:Coverages xmlns="http://www.opengis.net/ows/1.1"

xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:wcs="http://www.opengis.net/wcs/1.1" xmlns:ows="http://www.opengis.net/ows" xmlns:owcs="http://www.opengis.net/wcs/1.1/ows" xmlns:gml="http://www.opengis.net/gml" xsi:schemaLocation="http://www.opengis.net/ows/1.1 ../owsCoverages.xsd"><wcs:Coverage>

<ows:Abstract>Coverage created from GetCoverage operation request to a WCS

</ows:Abstract> <ows:Reference xlink:href="http://data.laits.gmu.edu:8080/NWGISS_Temp_Data/7bff494d-

0625-4ebd-a016-27336cc33306.he5" xlink:role="urn:ogc:def:role:WCS:1.1:coverage"/>

</wcs:Coverage> </wcs:Coverages>

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Discussion & Conclusion

• Aura/HIRDLS data can be served effectively through the combination of powerful HDF-EOS and WCS– WCS provides standard interfaces to enable the access of

Aura/HIRDLS data by geospatial applications.– WCS_T provide a transparent, standard mechanism for the

transaction of geospatial data in the Web environment.– This WCS can be consumed by other Web services easily

through its standard interfaces. It is realistic to chain different WCS into a complex composite service and better serve specific, advanced applications, e.g. application in sensor web project.

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Discussion & Conclusion

• The work in future– To complete other required operations (e.g. getcapabilities,

describeCoverage, transaction.)– Provide support for coverage request with BBox

parameters and one more coverage output.– Provide support for composing BBox and Temporal Period

request.

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Reference

1. OGC 06-083r8, 2006-10-17, “Web Coverage Service (WCS) Implementation Specification, Version: 1.1.0”.

2. OGC 2007-06-27, “Web Coverage Service (WCS) — Transaction operation profile, Version: 1.1.0”.

3. July 1, 2006, “A Short Guide for V 2.00 Level-2 Data from HIRDLS PI”, from http://daac.gsfc.nasa.gov/Aura/HIRDLS/documents/Short-guide-Level2data_InitialRelease.pdf .

4. "AutoChem Wiki." from http://en.wikipedia.org/wiki/Autochem. 5. OGC 00-106, “The OpenGIS® Abstract Specification Topic 6:

The Coverage Type and its Subtypes , Version 4 ”.6. 30 June 2006, “HIRDLS Version 2.0 Level 2 Data Description

Quality Documents”, from http://daac.gsfc.nasa.gov/Aura/HIRDLS/documents/HIRDLS_Data_Description_InitialRelease.pdf

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Acknowledgements

• This study has been supported by two NASA-funded projects: NASA AIST-QRS-06-0026 (PI: Dr. John F. Moses, Co-I: Dr. Liping Di, Dr. Wayne Feltz, Dr. Jason Brunner, Dr. Robert Rabin) and NASA AIST-05-0064 (PI: Dr. Liping Di, Co-I: Dr. James Smith, Dr. David Lary).

• This study is also partially supported by the National Basic Research Program (973 program) of China: 2006CB701300 (PI: Dr. Jianya Gong).



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Implementation of OGC Web Coverage Service Using HDF5/HDF-EOS5 as the Base File Format